Safety and arming mechanism



April 1968 R. GELMAN 3,376,820

SAFETY AND ARMING MECHANISM Filed Sept. 17, 1957 I8 22." j L Y j FIG JNVENTOR. ROBERT GELMAN United States Patent 3,376,820 SAFETY AND ARMING MECHANISM Robert Gelman, Levittown, Pa., assignor to the United States of America as represented by the Secretary of the Army Filed Sept. 17, 1957, Ser. No. 684,628 2 Claims. (Cl. 102-83) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to a safety and arming device for small mortar fuzes in a projectile and has for an object to provide such a device that is safe and more reliable than the prior devices have been. Another object is to provide such a mechanism in which the arming device is more nearly responsive to travel of a projectile to a position far enough away from the gun for its burst to be harmless to those around the gun. A further object is to provide fuzes for a projectile that will require a greater travel of the projectile away from the gun than has heretofore been possible in weapons of smaller size. Still another object is to provide an arming device that is simple, safer and capable of being used in a projectile for a small mortar.

'Heretofore safety and time delay in arming a fuze for such a projectile has involved the sequential operation of a series of leaf springs in order to obtain a desired time delay. Such springs have been found to be too quick in their action and not always as safe as is desired.

According to this invention, a greater time delay has been obtained by the use of sequentially operated angularly displaceable members, their angular acceleration bearing a relation to linear acceleration of a projectile and enabling a greater time interval to elapse between the firing of a gun from which the projectile is to be thrown and movement of a fuze rotor element to an armed position.

Referring to the drawing:

FIG. 1 is a right-side view of the device of this invention in its safe position.

FIG. 2 shows a side view of the same device, the leaf 17 in its raised position.

FIG. 3 is a top plan view of this same device in armed position.

FIG. 4 is a left-side view of the leaf 17 shown in FIG. 3.

FIG. 5 is a left-end view of the leaf shown in FIG. 4.

FIG. 6 is a view of the disc 18 showing a resilient pawl and ratchet teeth on the bottom of the said disc.

As shown in the drawing, FIG. 3, the device comprises a rotor 10 having a projection 34 thereon, shown in the armed position as being mounted on a shaft 11. A hole 12 extends through the rotor inasmuch as an initiator flame has to pass through this rotor and through the supporting base on which it is mounted. The right supporting wall 13 for the rotor shaft and the left supporting wall 14 mount the rotor 10 over the base or support 15. This base has a perforation 32, alined with the perforation 12. Electrical conductors 16 and 33 form a closed circuit upon the rotor being moved from its unarmed position shown in FIG. 1 into its armed position shown in FIG. 3. A first to move element or leaf 17 and a second to move element or disc 18 constitute angularly displaceable members capable of being actuated in sequence in order to release the rotor and allow it to be moved by its spring into the armed position of FIG. 3.

The base is provided with side recesses 19 and 20 for reception of lugs holding a cover fast to opposite side of the base 15.

A shaft 21 for the leaf 17 is mounted between the wall 13 and an outermost wall 25. A spring 22 around the shaft 21 cooperates with the base 15 and the shaft 21 to urge the leaf 17 to its armed position shown in FIG. 2. A weight 23 on the disc 18 enables the disc to have a clockwise angular displacement in response to setback. The disc 18 is later moved in a counterclockwise direction upon deceleration of the projectile. The disc 18 is mounted on the shaft 24 as shown in FIGS. 1 and 2 and this shaft is mounted between the supporting plates 25 and 13. An arcuate slot 28 in the leaf 17 enables the leaf to be raised by movement in a counterclockwise direction under influence of its spring 22 until the shaft 24 reaches the end of said slot. The end of the shaft 21 is provided with a slot 26 for reception of an end portion of the spring 22 urging this shaft 21 and its leaf 17 on reduction in setback to the upward position shown in FIG. 2. The left end of the shaft 21, shown in FIG. 3, is provided with a projection 27 having a cross section in the shape of a half-moon, FIG. 5. Projection 27 on shaft 21 cooperates with the projection 34 on the rotor 10 to retain the rotor in its unarmed position until the leaf 17 rotates during a reduction in setback.

A latch or spring pawl 29 is mounted on the base 15 (see FIG. 6) so that the pawl cooperates with ratchet teeth 30 in the disc 18.

In operation, with the parts in the safe or unarmed position shown in FIG. 1, the force of setback causes the leaf 17 to be moved downward and clockwise.compressing the spring 22 and engaging the spring pawl 29 thus releasing teeth 30 on the disc 18 and allowing said disc to rotate in a clockwise direction into the position shown in FIG. 2 from the position shown in FIG. 1. After the leaf 17 moves from the position shown in FIG. 1 in a clockwise direction to disengage pawl 29, the counter-weight 23 enables the disc 18 to be rotated in 'a clockwise direction due to setback as soon as pawl 29 has disengaged the ratchet teeth 30'. In such movement the clockwise motion of the disc 18 is stopped when the Weight'23 has been moved to the top edge of a ledge as shown in FIG. 2. The leaf 17 does not directly cause the disc 18 to be rotated, but after the leaf has descended from the position shown in FIG. 1 it has moved clear of the weight 23 on the disc 18 enabling the disc to be ready to rotate in a clockwise direction as soon as released by the pawl 29, as indicated. After releasing the spring pawl 29 to enable the disc 18 to be rotated under the force of setback, the disc may rotate an angular extent from about that shown in the drawing or to a larger value of as much as about After the disc 18 has rotated in the clockwise direction to a position shown in FIG. 2 the spring 22 causes the leaf 17 to be raised on reduction in setback to the position shown in FIG. 2, after which the disc 13 may also be moved upward upon deceleration of the projectile in which this arming device is placed. As soon as the leaf 17 has reached the position shown in FIG. 2 the halfmoon portion 27 has been moved into a position such that a cooperative projection 34 on the rotor 10 will be enabled to be released to cause the rotor to move under the force of the rotor spring 31 in a counterclockwise direction as viewed from the right of FIG. 3 until the perforation 12 has a substantially vertical axis. On reaching this armed position for the rotor shown in FIG. 3, electrical conductors 16 and 33 complete a circuit through an initiator or primer, allowing the fuze portion of the projectile to fire the same, causing a flame to pass into and through the perforation 12 in the rotor and through the also aligned perforation 3-2 in the base 15. This would normally occur considerably after the armed position is established. When the rotor 10 has reached its fully armed position shown in FIG. 3 an abutment, not shown, precludes further angular movement of the rotor, under its actuating spring 31.

Among the advantages of the present invention may be mentioned the fact that this arming device is the first one to be safe so far as is known under a 40 ft. drop test. Under the present invention the angular travel of first the leaf 17 downward, then the angular travel of the disc 18 in a clockwise direction moving the weight 23 downward, and finally the upward movement of the leaf 17 under its spring 22 on deceleration, provides sufficient time delay so that there is no chance of a burst occurring until after the projectile has left the barrel from which it has been fired, so that less danger exists of the personnel around the fired weapon being harmed by premature explosion. It is the movement of the leaf 17 to the armed position shown in FIG. 2 that unlocks the rotor 10 'and enables its spring 31 to move the rotor in a counterclockwise direction as viewed from the right in FIG. 3 and into the armed position. The acceleration to which a projectile is expected to be subjected is believed to be a value of in excess of 350 G5. The arming device is intended for a small mortar of about 80 mm. with an axial length for the 'arrning devices of about .71 inch and its diameter being about 1.575 inches. As shown in FIGS. 2 and 6 of the drawing, shaft 24 is of less diameter than the width of arcuate slot 28 to enable the leaf 17 to move under setback free of disc 18 and its shaft 24.

-I claim:

1. -In a fuse arming mechanism for a projectile operable under the force of set back, said fuse arming mechanism having a two position rotor movable between an unarmed position 'and an armed position, a shaft for said rotor, a support for said rotor shaft, a spring engaging said support and said rotor shaft for moving the rotor from said unarmed position to said armed position, said rotor having 'a hole therethrough for the passage of an initiator flame when said rotor is in said armed position, and an angularly movable retaining and releasing means for retaining said rotor and shaft in said unarmed position and releasing said rotor shaft for movement of said rotor by said spring to said armed position, the combination therewith of the improvement in said angularly movable retaining and releasing means whereby said fuse arming mechanism may be more nearly safe and more compact for use in small calibers of ammunition, said improvement including a leaf having a radially off-set center of gravity for rotation of said leaf under setback during acceleration of a projectile, said leaf being mounted adjacent said rotor and laterally displaced from a longitudinal axis of said rotor shaft, a shaft on which said leaf is mounted for rotation between two positions, means on said leaf shaft for retaining said rotor shaft in said unarmed position and for releasing said rotor shaft for rotation to said armed position, a spring engaging said leaf shaft and said support for moving said leaf to a position for releasing said rotor shaft, a disc, a shaft on which said disc is mounted adjacent a longitudinal axis of said leaf shaft and said rotor shaft, said disc shaft extending in the general direction of said leaf shaft and said rotor shaft, a counter-weight on said disc projecting from the plane of said disc to engage said leaf and retain said leaf and said leaf shaft against movement to a position in which said rotor retaining and releasing means operates, and means engaging said disc for retaining said disc against movement under set back and releasable by movement of said leaf under a predetermined set back whereby said leaf is moved under predetermined set back before said disc and said disc is moved under set back after said disc locking means has been released by said leaf, said weight on said disc moving clear of said leaf during movement of said disc under set back and on a reduction in set back said leaf shaft spring moving said leaf through said position in which said leaf is retained by said disc counter weight to a position in which said rotor shaft is released by said rotor releasing means, said rotor shaft spring moving said rotor to said armed ention on release of said rotor shaft by said rotor shaft retaining means whereby said rotor perforation can pass an initiator flame through said rotor and whereby said rotor, said leaf and disc may be mounted for movement in generally parallel adjacent planes.

2. A fuse arming mechanism according to claim 1 including a switch in a circuit to fire a fuse actuated by said arming mechanism, s'aid switch consisting of an electrical conductor on said rotor and an electrical conductor on said rotor shaft support, said electrical conductors contacting when said rotor is in said armed position for closing such a circuit to fire said fuse, whereby greater safety is obtained against premature firing.

References Cited UNITED STATES PATENTS 2,486,362 10/1949 OBrien 102 78 X 2,537,953 1/1951 Andrews 102-78 2,586,437 2/1953 Rabinow 102-78 FOREIGN PATENTS 714,540 9/1954 Great Britain.

BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL BOYD, ARTHUR M. HORTON, Examiners.

W. J. NELSON, G. H. GLANZMAN,

Assistant Examiners. 

1. IN A FUSE ARMING MECHANISM FOR A PROJECTILE OPERABLE UNDER THE FORCE OF SET BACK, SAID FUSE ARMING MECHANISM HAVING A TWO POSITION ROTOR MOVABLE BETWEEN AN UNARMED POSITION AND AN ARMED POSITION, A SHAFT FOR SAID ROTOR, A SUPPORT FOR SAID ROTOR SHAFT, A SPRING ENGAGING SAID SUPPORT AND SAID ROTOR SHAFT FOR MOVING THE ROTOR FROM SAID UNARMED POSITION TO SAID ARMED POSITION, SAID ROTOR HAVING A HOLE THERETHROUGH FOR THE PASSAGE OF AN INITIATOR FLAME WHEN SAID ROTOR IS IN SAID ARMED POSITION, AND AN ANGULARLY MOVABLE RETAINING AND RELEASING MEANS FOR RETAINING SAID ROTOR AND SHAFT IN SAID UNARMED POSITION AND RELEASING SAID ROTOR SHAFT FOR MOVEMENT OF SAID ROTOR BY SAID SPRING TO SAID ARMED POSITION, THE COMBINATION THEREWITH OF THE IMPROVEMENT IN SAID ANGULARLY MOVABLE RETAINING AND RELEASING MEANS WHEREBY SAID FUSE ARMING MECHANISM MAY BE MORE NEARLY SAFE AND MORE COMPACT FOR USE IN SMALL CALIBERS OF AMMUNITION, SAID IMPROVEMENT INCLUDING A LEAF HAVING A RADIALLY OFF-SET CENTER OF GRAVITY FOR ROTATION OF SAID LEAF UNDER SETBACK DURING ACCELERATION OF A PROJECTILE, SAID LEAF BEING MOUNTED ADJACENT SAID ROTOR AND LATERALLY DISPLACED FROM A LONGITUDINAL AXIS OF SAID ROTOR SHAFT, A SHAFT ON WHICH SAID LEAF IS MOUNTED FOR ROTATION BETWEEN TWO POSITIONS, MEANS ON SAID LEAF SHAFT FOR RETAINING SAID ROTOR SHAFT IN SAID UNARMED POSITION AND FOR RELEASING SAID ROTOR SHAFT FOR ROTATION TO SAID ARMED POSITION, A SPRING ENGAGING SAID LEAF SHAFT AND SAID SUPPORT FOR MOVING SAID LEAF TO A POSITION FOR RELEASING SAID ROTOR SHAFT, A DISC, A SHAFT ON WHICH SAID DISC IS MOUNTED ADJACENT A LONGITUDINAL AXIS OF SAID LEAF SHAFT AND SAID ROTOR SHAFT, SAID DISC SHAFT EXTENDING IN THE GENERAL DIRECTION OF SAID LEAF SHAFT AND SAID ROTOR SHAFT, A COUNTER-WEIGHT ON SAID DISC PROJECTING FROM THE PLANE OF SAID DISC TO ENGAGE SAID LEAF AND RETAIN SAID LEAF AND SAID LEAF SHAFT AGAINST MOVEMENT TO A POSITION IN WHICH SAID ROTOR RETAINING AND RELEASING MEANS OPERATES, AND MEANS ENGAGING SAID DISC FOR RETAINING SAID DISC AGAINST MOVEMENT UNDER SET BACK AND RELEASABLE BY MOVEMENT OF SAID LEAF UNDER A PREDETERMINED SET BACK WHEREBY SAID LEAF IS MOVED UNDER PREDETERMINED SET BACK BEFORE SAID DISC AND SAID DISC IS MOVED UNDER SET BACK AFTER SAID DISC LOCKING MEANS HAS BEEN RELEASED BY SAID LEAF, SAID WEIGHT ON SAID DISC MOVING CLEAR OF SAID LEAF DURING MOVEMENT OF SAID DISC UNDER SET BACK AND ON A REDUCTION IN SET BACK SAID LEAF SHAFT SPRING MOVING SAID LEAF THROUGH SAID POSITION IN WHICH SAID LEAF IS RETAINED BY SAID DISC COUNTER WEIGHT TO A POSITION IN WHICH SAID ROTOR SHAFT IS RELEASED BY SAID ROTOR RELEASING MEANS, SAID ROTOR SHAFT SPRING MOVING SAID ROTOR TO SAID ARMED POSITION ON RELEASE OF SAID ROTOR SHAFT BY SAID ROTOR SHAFT RETAINING MEANS WHEREBY SAID ROTOR PERFORATION CAN PASS AN INITIATOR FLAME THROUGH SAID ROTOR AND WHEREBY SAID ROTOR, SAID LEAF AND DISC MAY BE MOUNTED FOR MOVEMENT IN GENERALLY PARALLEL ADJACENT PLANES. 